<i>Catalyst<i> is a professional learning tool intended to bring to life the findings of a collaborative research and development project carried out between researchers at the UCL Institute of Education and Challenge Partners, an informal national network of schools. <br> <br> The project investigated four questions: What is it about effective middle leadership within and across schools that changes teachers' practice? What are the most powerful ways of sharing knowledge about excellent middle leadership practice within and across schools? What are the most important factors when designing evidence-based tools to track changes in teachers' practice as a result of middle leaders' interventions? What leadership conditions in schools help develop and embed cultures of shared outstanding practice? <br> <br> The collection consists of two sets of resource cards and a clear and detailed facilitator guide, and has been designed for use by staff in schools in all contexts and across the entire student age range. Ultimately, the aim of the<i> Catalyst </i> process is to: help develop better understanding of and skills in teacher/middle leadership stimulate evidence-informed conversations about teacher/middle leadership which lead to deep and meaningful learning support skilled facilitation of these conversations encourage inquiry, improve problem-solving and enrich decision-making through collaboration enhance leadership within schools and across networks and school partnerships. <br><br><b>About the Authors</b><br><br> A Professor in Education at Durham University, Chris Brown is seeking to drive forward the use of professional learning networks to promote the collaborative learning of teachers. Chris also has a long-standing interest in how research evidence can and should, but often doesn't, aid the development of education policy and practice. <br> <br> A former teacher and school leader, Karen Spence-Thomas is now a programme leader for Bespoke Leadership Programmes at UCL IOE. She specialises in designing and facilitating tailored professional development programmes for leaders within and across schools both in the UK and internationally, and co-leads the IOE's Research and Development Network of schools. <br> <br> Louise Stoll is Professor of Professional Learning at UCL Institute of Education (IOE) and an international consultant, focusing on how schools and systems create capacity for learning. Louise has co-developed several materials and tools to support leaders and teachers in collaboratively connecting research evidence and practice. <br> <br> Carol Taylor is a programme leader for Bespoke Leadership Programmes at UCL IOE. A former school leader, she helps schools to embed practitioner research and inquiry into organisational and individual practice. Carol also designs and facilitates bespoke leadership programmes for national and international contexts.